Chargers are adopted to control charging process to batteries. Normally, a switching charger works under a constant current mode firstly, and then works under a constant voltage mode. A prior art switching charger controls a current flowing through an inductor in a hysteretic window to achieve the constant current mode. FIG. 1 schematically shows a prior art switching charger. As shown in FIG. 1, a control circuit 100 detects a current flowing through an inductor L to generate a current sense signal Ics. Meanwhile, the control circuit 100 receives a feedback signal Vfb indicating a charging voltage Vbatt via a voltage divider consisting of resistors R1 and R2. Based on the current sense signal Ics and the feedback signal Vfb, the control circuit 100 generates a control signal G1 to control the power switches M1 and M2, so as to control charging process to the load, i.e., the battery. However, the switching frequency of the prior art switching charger varies in a wide range and is not suitable for some applications.